The invention relates to the field of exploration and operation of oil or gas fields in which rotary drill stems are used. A drill stem may comprise pipes, heavy weight drill pipes, drill collars, stabilizers or couplings. The pipes are assembled end to end by makeup into a pipe string which constitutes a substantial or even dominant portion of the length of the drill stem. More particularly, the invention relates to a profiled part for rotary drilling equipment such as a pipe disposed in a rotary drill pipe string.
The characteristics of a drill stem, and more generally an element of a drill stem, contribute to the fundamental properties of quality, performance and safety of the general drilling process both during the excavation phases proper and also during phases involving maneuvers between the bottom and the surface.
Advances in hydrocarbon exploration demand making trajectory profiles which are becoming more and more complex under geological conditions which are becoming more and more extreme. Currently, exploration for hydrocarbons is being carried out at depths which are routinely over 4 km with departures with respect to the fixed facility which may exceed ten kilometers. The invention envisages a drill stem element that is in particular adapted for deviated wells, i.e. wells wherein the inclination to the vertical or the horizontal direction can be varied during drilling. Deviated wells can currently reach depths of the order of 2 to 8 km and horizontal distances of the order of 2 to 15 km.
In the case of deviated wells comprising practically horizontal sections, the frictional torques due to rotation of the pipe strings in the well may reach very high values during drilling. The frictional torques may compromise the equipment used or the drilling targets. Further, pulling out the spoil produced by drilling is very often difficult because of sedimentation of the debris produced in the drilled hole, in particular in the portion of the drilled hole that is steeply inclined with respect to the vertical. This results in poor cleaning of the hole and an increase in both the coefficients of friction of the pipes of the pipe string inside the drilled well and the contact surfaces between the pipes and the well walls.
Document FR 2 824 104 discloses a profiled element for rotary drilling equipment comprising a zone for bearing on the wall of the drilled hole, a turbulence zone in order to activate the movement of the drilling fluid in the drilled hole around the drilling equipment, and a deflection zone adjacent to the bearing zone and to the turbulence zone extending in the axial direction of the profiled element and comprising at least one surface which is inclined with respect to the drilling axis, the meridian line of which in an axial plane moves away from the axis of the profiled element in the direction moving from bottom to top in the service position of the profiled element in the drilled hole.
Further, document WO-2009-115687 discloses a drill stem element comprising at least one zone for bearing on the wall of the drilled hole, the bearing zone being provided with at least one bearing section with an external diameter which is greater than the diameter of the other portions of the element, and two activation zones substantially adjacent to the bearing zone and disposed upstream and downstream of said bearing zone.
That type of device has proven satisfactory until recently. However, a need has arisen for lighter weight as well as lower rigidity drill stems while maintaining or even improving pull-out, with the drilling fluid, of debris generated by formation of the hole. In particular, there is a need whereby any improvement in existing drill stems must maintain the pressure drops observed in the drilling fluid below acceptable thresholds in order to avoid clogging by debris becoming caked between the drilled hole and the stem. There is also a need for reducing the manufacturing costs of such drill stems and in particular of simplifying manufacture. Finally, there is a need to homogenize the speed of the drilling fluid right along the stem in order to prevent the hole from blocking up as much as possible.